Vertical rotor braze joint with retention chamfer

ABSTRACT

The present invention relates to a rotor shaft and rotor body assembly in an x-ray device, and it method of manufacture, that resists the formation of cracks in the braze joint due to the elimination of horizontal shear planes therein. The inventive structure also comprises an enlarged proximal end of the rotor shaft and an inventive assembly method that prevents the rotor shaft from de-coupling from the rotor body should the braze material entirely fail during field use.

BACKGROUND OF THE INVENTION

1. The Field of the Invention

The present invention relates to x-ray tubes having rotating anodestructures. In particular, embodiments of the present invention relateto structures and assembly methods for a rotor shaft and rotor bodyassembly of an x-ray tube rotating anode.

2. The Relevant Technology

X-ray producing devices are extremely valuable tools that are used in awide variety of applications, both industrial and medical. Suchequipment is commonly used in areas such as diagnostic and therapeuticradiology; semiconductor manufacture and fabrication; and materialstesting.

The basic operation of typical x-ray producing equipment is similar. Ingeneral, x-rays, or x-radiation, are produced when electrons arereleased, accelerated, and then stopped abruptly. A schematicrepresentation of a typical x-ray tube is shown in FIG. 1. Theillustrated x-ray tube assembly 1 includes three primary elements: acathode 2, which is the source of electrons; an anode 3, which isaxially spaced apart from the cathode and oriented so as to receiveelectrons emitted by the cathode; and a voltage generation element forapplying a high voltage potential to accelerate the electrons from thecathode to the anode.

The three elements are usually positioned within an evacuated housing 4.An electrical circuit is connected so that the voltage generationelement can apply a high voltage potential (ranging from about tenthousand to in excess of hundreds of thousands of volts) between theanode (positive) and the cathode (negative). The voltage differentialcauses the electrons that are emitted from the cathode 6 to form a beamand accelerate towards an x-ray “target” that is positioned on thesurface of a anode disk 5. The target surface (sometimes referred to asthe focal track) is comprised of a refractory metal, and when theelectrons strike the target at the focal spot, the kinetic energy of thestriking electron beam is converted to electromagnetic waves of veryhigh frequency, i.e., x-rays. The resulting x-rays emanate from theanode target, and are then collimated through a window 9 for penetrationinto an object, such as an area of a patient's body. As is well known,the x-rays that pass through the object can be detected and analyzed soas to be used in any one of a number of applications, such as x-raymedical diagnostic examination or material analysis procedures.

In addition to producing x-rays, when the electrons impact the targetsurface much of the resulting energy is converted to heat. This heat,which can reach extremely high temperatures, is initially concentratedin the anode target and then dissipated to other areas of the x-raytube. These high operating temperatures can damage the x-ray tube,especially over time.

The anode disk 5 (also referred to as the rotary target or the rotaryanode) is rotatably mounted on a rotating nose piece or stem androtating shaft 11, which is connected to a supporting rotor assembly 7.The disk 5, shaft and rotor assembly are rotated by a suitable means,such as a stator motor 8. The disk is typically rotated at high speeds(often in the range of 10,000 RPM), thereby causing the focal track torotate into and out of the path of the electron beam. In this way, theelectron beam is in contact with specific points along the focal trackfor only short periods of time, thereby allowing the remaining portionof the track to cool during the time that it takes the portion to rotateback into the path of the electron beam.

It will be appreciated that the need to continuously accelerate androtate the disk at such high speeds in the presence of extremely hightemperatures can give rise to a number of problems. For instance, whilethe rotation of the track helps reduce the amount and duration of heatdissipated in the anode target, the focal track is still exposed to veryhigh temperatures—often temperatures of 2500° C. or higher areencountered at the focal spot of the electron beam. This heat istransferred to other portions of the x-ray tube assembly, including theshaft and rotor assembly, resulting in extreme thermal stresses at theinterfaces between the various structures. Moreover, acceleration anddeceleration of the relatively heavy anode disk results in severemechanical stresses being imposed on the rotor assembly. Unfortunately,the structures and assembly methods used for anode disk rotationalassemblies have not been entirely satisfactory in addressing the variousproblems arising from such mechanical and thermal stresses.

For example, a rotor shaft and rotor body assembly have typically beeninterconnected by way of threads formed on an outer portion of therotor, which is then received within a corresponding threaded boreformed within a portion of the rotor body. In addition, a brazed jointmay be applied between the threaded mating surfaces. Also, a screw, pin,or the like may be used to secure the rotor shaft to the rotor, whichassures that the rotor shaft does not detach from the rotor body in theevent that the threaded engagement/braze joint fails. Finally, the rotorshaft may be further welded to rotor body by use of an electron beamwelding method.

It will be appreciated these types of manufacturing steps are timeconsuming, expensive, and can result in an assembly with multiple pointsof potential failure. For instance, the formation of a threaded rotorshaft and corresponding mating rotor body, along with the placement of ascrew or the like, entails intensive machining and assembly.Additionally, the placement of a screw or similar fastening means mayitself be an operation that is subject to occasional defects. Also,electron beam welding can cause brittleness at the weld that may lead tostructural failure, which is made even more likely due the extremetemperature fluctuations that are encountered during operation of thex-ray tube. Finally, each of these techniques entail expensive and timeconsuming manufacturing steps, which increase the overall productioncost of the x-ray tube device.

The types of materials that are typically used in the construction of arotor shaft and rotor body can also give rise to problems. For instance,to restrict the flow of heat by conduction into the rotor shaft androtor body assembly from the rotating anode target disk, the rotor shaftis often provided with a minimum cross-sectional size and is generallymade of a relatively poor heat conductive material, such as a molybdenumalloy called TZM. TZM comprises about 99% molybdenum with the balancemaking up various proportions of titanium and zirconium. While the TZMmaterial exhibits superior structural strength, it can have a differentlinear coefficient of thermal expansion than the material making uprotor body 14. For instance, the rotor body is often made of an ironalloy such as Incoloy 909 sold by Inco Alloys International Inc. ofHuntington, W. Va., which has a linear thermal expansion coefficientthat is slightly different from that of TZM. This can give rise tosignificant structure-weakening events during operation, due to thevarying rate of thermal expansions of the two materials.

Also, where the rotor body is constructed of iron or an iron alloymaterial, the extreme temperature fluctuations can cause such aniron-based alloy to experience allotropic transformation from bodycentered cubic (bcc) to face centered cubic (fcc). For instance, whenrising through about 912° C., iron transforms from bce to fcc andconsequently shrinks in volume. Therefore, in addition to disparatelinear thermal expansion coefficients, allotropic transformations causeadditional stress upon a braze joint at the interface between rotorshaft and rotor body.

Many of these problems can be manifested during repeated operation ofthe x-ray tube. During operation, the rotor shaft begins to heat up andmechanical stresses from high rotational speeds are imposed. Forinstance, when the rotor shaft is connected to the rotor assembly with athreaded interface and a braze joint, a horizontal thermal shear planeis often produced at the threaded interface between the shaft and therotor body within the braze joint. This thermal shear stress can betransferred through the braze material. Moreover, the condition isexacerbated if rotor body 14 is made of iron or an iron alloy, and istaken through the allotropic transformation temperature threshold ofabout 912° C., as noted. Over time, this continuous cycle of expansionand contraction can result in a cracks or other failure points in thejoint. Once a crack has nucleated, propagation of the crack typicallyresults, ultimately resulting in failure of the x-ray tube.

Other problems can also result when traditional methods are used tointerconnect the rotor assembly. For instance, the braze joint is oftencomprised of a braze material that will readily flow along and betweenthe threaded surfaces of the rotor shaft and the rotor body. In theevent that the braze material has a melting temperature above 1150° C.,the molybdenum component of the TZM material forming the rotor shaftforms a eutectic with the metal component of the brazing material, thatin turn produces an intermetallic compound. This compound can be brittlein comparison to most metals at room temperature, and can become moreductile as the temperature increases, where conventional metals may tendto allotropically transform and fail or even reach liquidustemperatures. Alternatively, if the braze material has a meltingtemperature below about 900° C., the braze joint may soften duringoperation of the x-ray tube and fail to withstand the resultingmechanical stresses.

Thus, what is needed is a rotor shaft and rotor body assembly thatovercomes the problems of the prior art. In particular, it would beadvantageous to have a rotor shaft and rotor body assembly that areinterconnected in a manner so as to better withstand the extremely hightemperatures and mechanical stresses imposed during operation of thex-ray tube. Additionally, it would be advantageous to provide a rotorshaft and rotor body assembly that are interconnected in a manner so asto resist cracking within the braze joint. Also, it would beadvantageous to provide a interconnection scheme that is easy and low incost to implement and manufacture.

SUMMARY AND OBJECTS OF THE INVENTION

It is therefore a primary object of the invention to provide a rotorshaft and rotor body assembly that overcomes the problems of the priorart, namely, to provide an assembly that is better able to withstand themechanical and thermal stresses generated in an operating x-ray tube. Itis also an object of embodiments of the invention to provide a rotorshaft and rotor body assembly that substantially eliminates the presenceof horizontal thermal shear planes in the braze between a rotor shaftand rotor body assembly. Still another object of embodiments of thepresent invention is to provide a rotor shaft and rotor body assemblyhaving a rotor shaft that is implemented so as to resist decoupling fromthe rotor body, even in the presence of high temperatures, highoperational speeds, and repeated and prolonged operation. It is also anobject of the present invention to provide a method of assembling arotor shaft and rotor body that is simplified, and that uses fewercomplex and time consuming assembly steps.

These and other objectives are addressed by the present invention, whichrelates to a rotor shaft and rotor body assembly that maintainsstructural integrity through extreme temperature fluctuations, and inthe presence of severe mechanical stresses. As noted, in a rotatinganode x-ray tube, a rotor shaft and rotor body assembly experiencestemperature changes between room temperature and 1,000° C. and higherduring routine usage. Moreover, the assembly is subjected to dramaticmechanical stresses resulting from the high rotational speeds. In onepreferred embodiment of the present invention, these problems areaddressed with a rotor shaft and rotor body assembly that eliminates theoccurrence of horizontal thermal shear planes that are otherwise presentat connection points between the shaft and rotor body in the prior art.The assembly also eliminates catastrophic decoupling of the rotor shaftand rotor body, without the use of a screw or the like.

A first embodiment of the present invention includes a rotor shafthaving an end that has an enlarged convex profile such as a chamfer or aflange. Formed within a corresponding end of the rotor body is an innerbore or recess that has an enlarged concave profile that iscomplimentary in size and shape to the rotor shaft enlarged convexprofile. When assembled, the shaft chamfer or flange on the shaft ismatingly received within the recess of the rotor body. In the preferredembodiment, a braze joint is then formed between the mated rotor shaftend and the recess of the rotor body. Moreover, the orientation of theshaft and rotor ensure that the braze joint is predominantly axiallydisposed between the shaft and the rotor body. Also, the braze joint canbe formed to be substantially vertical, thereby eliminating anyhorizontal thermal shear planes between the shaft and the rotor joint.Various other embodiments vary the shape, size and/or configuration ofthe rotor shaft end and the corresponding mating surface within therotor body. These various configurations provide different attachmentcharacteristics, and allow for different types of braze jointconfigurations.

Embodiments of the present invention also include a method of assemblinga rotor body and a rotor shaft system. For instance, one assembly methodcomprises the insertion of a distal end of the rotor shaft entirelythrough a bore formed within the rotor body until the enlarged convexprofile of the rotor shaft seats against the complimentary contour ofthe recess found within the rotor body. The two ends can then be affixedwith the application of a braze joint.

These and other objects, features and advantages of the presentinvention will become more fully apparent from the following descriptionand appended claims, or may be learned by the practice of the inventionas set forth hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the manner in which the above-recited and other advantagesand objects of the invention are obtained, a more particular descriptionof the invention briefly described above will be rendered by referenceto a specific embodiment thereof which is illustrated in the appendeddrawings. Understanding that these drawings depict only typicalembodiments of the invention and are not therefore to be considered tobe limiting of its scope, the invention will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1 is a cut-away perspective view of a conventional x-ray tubeassembly;

FIG. 2 is an exploded perspective view of one presently preferredembodiment of a rotor shaft and rotor body assembly, wherein a cut-awayview of the rotor body reveals a rotor body inner bore and a rotor bodyouter bore that are separated by a rotor shaft chamfer seat;

FIG. 3 is a cut-away perspective view of the rotor shaft and rotor bodyassembly of FIG. 2, wherein it can be seen that the rotor shaft chamferis disposed against the rotor body chamfer seat in preparation forbrazing by melting of a braze ring;

FIG. 4 is a detail section taken from FIG. 3, wherein the assembly isillustrated at the braze joint;

FIG. 5 is a detail section taken from FIG. 3, wherein an alternativeembodiment is illustrated at the braze joint;

FIG. 6 is a detail section taken from FIG. 3, wherein yet anotheralternative embodiment is illustrated at the braze joint;

FIG. 7 is a detail section taken from a structure similar to thelocation depicted in FIG. 3, wherein an alternative embodiment isillustrated to demonstrate a vertical braze joint with no horizontal ordiagonal braze joints present;

FIG. 8 is a detail section taken from a structure similar to that seenin FIG. 3, wherein an alternative embodiment depicts a vertical brazejoint and a close contact between a chamfer and chamfer seat thatrestrict the flow of braze material therebetween;

FIG. 9 is a detail section taken from a structure similar to that seenin FIG. 3, wherein an alternative embodiment illustrates a rotor bodyv-notch that acts as a stop or braze material well in order to achieve avertical braze joint with no horizontal shear structures;

FIG. 10 is a detail section taken from a structure similar to thatdepicted in FIG. 3, wherein an alternative embodiment illustrates aflange at the proximal end of a rotor shaft and a v-notch cut into therotor body that acts as a stop or well for braze material during thebrazing of the shaft to the body; and

FIG. 11 is a detail section taken from a structure similar to thatdepicted in FIG. 3, wherein an alternative embodiment depicts a rotorshaft v-notch cut above the chamfer that acts as a braze material stopor well in order to achieve a vertical braze joint according to thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention relates to a rotor shaft and rotor body assemblysuitable for use in a x-ray device having a rotating anode. Inparticular, presently preferred embodiments significantly reduce oreliminate thermal expansion and contraction shear stresses in the brazedinterface between the shaft and the rotor body. In addition, embodimentsof the present invention also provide an improved interconnectionbetween the rotor shaft and the rotor body assembly that resistsdecoupling in the event of a catastrophic failure of the braze materialbetween the two components.

Reference will now be made to the drawings wherein like structures willbe provided with like reference designations. It is to be understoodthat the drawings are diagrammatic and schematic representations ofpresently preferred embodiments of the present invention, and are notnecessarily drawn to scale.

FIG. 2 is a perspective view of a presently preferred embodiment of adisassembled rotor shaft and rotor body assembly 110 constructed inaccordance with teachings of the present invention. The rotor shaft andthe rotor body assembly 110 comprise a cylindrical rotor shaft 112having a reduced diameter towards the distal end 140, and an enlargeddiameter towards the proximal end 154. Formed at the distal end 154 is arotor shaft chamfer section 156. Formed within rotor shaft 112 is bore130, as is designated via phantom lines. Also shown is a rotor body 114,which is also cylindrical in shape. A cut-away view of rotor body 114reveals a rotor body inner bore 136 and a rotor body outer bore 138,axially disposed within rotor body 114, and separated by a rotor shaftchamfer seat 164.

Assembly of the rotor shaft 112 and the rotor body 114 of FIG. 2requires the rotor shaft 112 to pass through rotor body 114 with thedistal end 140 first, from below the rotor body 114.

The rotor shaft chamfer 156 has a diameter that exceeds the diameter ofrotor body inner-bore 136. Consequently, when the rotor shaft 112 distalend 140 is passed through rotor body outer bore 138, past rotor shaftchamfer seat 164, the rotor shaft chamfer 156 seats against rotor shaftchamfer seal 164. For dimensional analysis purposes, the dimensionsdepicted in FIG. 4 are in arbitrary units, but they may be considered tobe in inches by way of non-limiting example.

In a preferred embodiment, rotor shaft 112 is made of molybdenum or amolybdenum alloy called TZM or another refractory or alloy. TZMcomprises about 99% molybdenum with variable fractional percentages oftitanium and zirconium. The TZM material exhibits superior structuralstrength to pure molybdenum material, it is easier to machine, and itwithstands the centrifugal stresses imposed upon it during rotation andcycling through a thermal change from approximately room temperature toabout 900° C. and above, returning to room temperature.

FIG. 3 illustrates the rotor shaft and rotor body assembly 110 in anelevational cut-away cross section immediately prior to brazing therotor shaft 112 to the rotor body 114. It can be seen that the interfacebetween the rotor shaft 112 and the rotor body 114 is entirely devoid ofany horizontal thermal shear planes. In this embodiment, the lack of anyhorizontal thermal shear planes is made possible by the interface of theright-cylinder shape of the rotor shaft main section 142 within therotor body inner bore 136 and the diagonal, frusto-conical interfacebetween the rotor shaft chamfer seat 164 and the rotor shaft chamfer156. A braze ring 168 is depicted as sitting against the rotor shaftmain section 142 and simultaneously sitting upon proximal surface 148 ofthe rotor body 114 adjacent the rotor shaft main section 112.

In order to achieve a reliable braze joint between the rotor body 114and the rotor shaft 112, it is preferable to configure respectivediametric sizes that provide an interposed gap when the rotor shaft 112is fully inserted upwardly through the rotor body 114 until the rotorshaft chamfer 156 seats against the rotor shaft chamfer seat 164. In apresently preferred embodiment, the gap that forms the interface betweenthe rotor shaft 112 and the rotor body 114 may have a dimension in therange of about 100 mils to about 1,000 mils in order to provide spacingthat will facilitate capillary action wetting as braze ring 168liquefies and fills into the gap to form the braze. Various suitablebraze materials are well known in the art. Examples of preferred brazingmaterials may be found in U.S. Pat. Nos. 4,736,400 and 4,969,172, thedisclosures of which are incorporated herein by specific reference.Preferably, the brazing material has a melting temperature so that itdoesn't melt under ordinary operating temperatures of the x-ray tube.The brazing material may also be a composition that forms anintermetallic with rotor shaft 112 and/or rotor body 114. At roomtemperature, an intermetallic composition is brittle relative totraditional metals, but at elevated temperatures where traditionalmetals begin to soften and/or melt, an intermetallic begins to behave asa traditional metal with favorable ductility, tensile, and compressivequalities at operating temperatures in the range from about 700° C. toabout 1,200° C. and higher.

In an alternative embodiment of the present invention, the rotor shaftand the rotor body assembly 110, depicted in FIG. 3, is assembledentirely without braze material. Tolerances are chosen between theconvex right-cylinder interface of the rotor shaft main section 142 andthe concave right-cylinder shape of the rotor body inner bore 136 suchthat the rotor shaft and rotor body assembly 110 can be assembled onlyby applying force to push the rotor shaft 112 into the rotor body innerbore 136, and thereby provide a tight and frictionally secure fitbetween the two.

Another preferred method of making the rotor shaft and rotor bodyassembly 110 without the presence of a braze material is to heat therotor body 114 to a temperature sufficiently high such that thermalexpansion allows for rotor shaft 112 to pass substantially through rotorbody inner bore 136 until the chamfer 156 abuts against rotor shaftchamfer seat 164. As the rotor body 114 cools, the interface between therotor shaft 112 and the rotor body 114 become increasingly tight due tothe thermal contraction of rotor body 114. Once the rotor shaft androtor body assembly 110 have substantially cooled to room temperaturefollowing assembly, field use thereof will not substantially diminishthe tightness of the fit of the rotor shaft 112 within the rotor bodybecause both the rotor shaft 112 and the rotor body will be heated andcooled substantially as a unit. In this embodiment, a failure of rotorshaft and rotor body assembly 110 would require either the rotor body114 to crack under tensile stress or the rotor shaft 112 to crack undercompressive stress. Preferred temperature differentials between therotor body 114 and the rotor shaft 112 for this type of assembly processare in a range from about 0° C. to 900° C., and in a preferredembodiment are between about 200° C. to about 350° C. The coefficient ofstatic friction between the rotor shaft 112 and the rotor body 114 issufficient to hold assembly 110 together, similar to the use of thebraze material. As an alternative embodiment, brazing may be done inaddition to the tight fit.

FIG. 4 is a detail section taken along the dashed line 4—4 from FIG. 3,in which it can be seen that a vertical braze joint 170 and a diagonalbraze joint 172 form a continuous braze interface between the rotorshaft 112 and the rotor body 114 beginning at the proximal surface 148where braze ring 168 (see FIG. 3) was located, and ending approximatelyat rotor shaft proximal end 154.

In comparison to the type of braze joints utilized in the prior art anddiscussed above, no horizontal thermal shear plane is present betweenthe shaft 112 and the rotor body 114. Additionally, as the rotor shaft112 heats by conduction from the rotating anode target disk, thermalexpansion of the rotor shaft 112 exerts only a compressive stress uponthe braze at vertical braze joint 170. Similarly, during temperatureescalation of the rotor shaft and rotor body assembly 110, and where therotor body 114 experiences an allotropic phase transformation from bccto fcc, additional non-shear stresses upon the vertical braze joint 170may be experienced.

It can be seen that a diagonal braze joint 172 completes the braze thatconnects the rotor shaft 112 with the rotor body 114. The diagonal brazejoint 172 may carry a horizontal thermal shear component that isproportional to the compressive stress in the vertical brazed joint 170multiplied by the cosine of the angle α. The total amount of horizontalthermal shear experienced between the rotor shaft chamfer 156 and therotor shaft chamfer seat 164 is minimal and substantially nondestructivecompared to stresses existing in structures of the prior art. Onepossible reason for this is that the heating of the rotor body 114begins substantially at the proximal surface 148 across vertical brazejoint 170, and then continues downward in both the rotor shaft 112 andthe rotor body 114. This heat conduction pattern ensures that thethermal gradients within the diagonal braze joint 172 causesubstantially only compressive stresses to occur.

The angle α designated in FIG. 4 defines the contour of the rotor shaftchamfer 156 in relation to the axial configuration of the rotor shaftmain section 142. The angle may be varied to minimize a horizontalthermal shear component within diagonal braze joint 172. For instance,as the angle α becomes larger and approaches 90°, any horizontal thermalshear component within diagonal braze joint 172 approaches zero. Inpresently preferred embodiments, the value for angle α is in a rangefrom about 30° to about 80°, and in one embodiment is in a range fromabout 60° to about 70°.

A primary purpose for the rotor shaft chamfer 156 is to retain the rotorshaft 112 within the rotor body 114, even in the event that the braze170 or 172 fails due to a crack. As such, the angle α need only be anyangle less than 90° that will facilitate retention of rotor shaft 112within rotor body 114 under the operating conditions of the particularx-ray device. Rotor shaft chamfer 156, with the above-discussedconfigurations of angle α, is one example of a means for retaining therotor shaft in the rotor body.

FIG. 5 illustrates another embodiment of the present invention, whichillustrates how the size and shape of the rotor shaft chamfer may bevaried in its vertical height, v, and in its horizontal extension, h, inrelation to the rest of the rotor shaft. In FIG. 5, the rotor shaft 212has a rotor shaft chamfer 256 that originates substantially at the sameheight as the proximal surface 248 of the rotor body 214, and thatterminates at the rotor shaft proximal end 254. The vertical height, v,of the rotor shaft chamfer 256 corresponds to the distance between therotor shaft proximal end 254, and the rotor body proximal end 258, whichis also at the same height as the proximal surface 248. A diagonal brazejoint 272 comprises the entire braze that attaches the rotor shaft 212to the rotor body 214. Again, the angle α determines the amount of ahorizontal thermal shear component that may be experienced within thediagonal brazed joint 272. Where the horizontal extension, designated ash, is sufficiently small such that angle α approaches 90°, anyhorizontal thermal shear component experienced within the diagonal brazejoint 272 approaches zero. Where the vertical height v of rotor shaftchamfer 256 begins at rotor shaft proximal end 254 and terminates at thelevel of the rotor body proximal end 258, the angle α may be small. Forexample, in this illustrated embodiment angle α may be in a range fromabout 30° to about 89°, and preferably is from about 60° to about 89°.

FIG. 6 is a detail section taken from a structure at a location similarto that taken from FIG. 3, and illustrates another embodiment of thepresent invention. Here, the vertical height v of the diagonal brazejoint 372 depicted between the rotor shaft chamfer 356 and the rotorbody chamfer seat 364 is minimized due to the relatively larger heightof a vertical braze joint 370. Diagonal braze joint 372 is thereforepresent as a minor portion of the braze. In this embodiment, verticalheight, v of the rotor shaft chamfer 356 is minimized and angle α ismaximized to approach 90°. While the structure depicted in FIG. 6 maynot have the same capability to retain rotor shaft 312 upon catastrophicfailure of the braze, it does minimize the extent of diagonal brazejoint 372 and therefore minimizes any horizontal thermal shear componentthat may occur therewithin. In one preferred embodiment, vertical heightv has a value of approximately 0.022 inches, and angle α has a value ina range from about 45° to about 89°, and preferably is between about 75°to about 89°.

The rotor shaft chamfer in connection with the rotor body may beimplemented with other structures. FIG. 7 is a detail sectionillustrating one such embodiment. In FIG. 7, an amount of a brazematerial is provided to form a vertical braze joint 470, which stops ator before the braze material makes contact with rotor shaft chamfer seat164. To do so, the cross-sectional area of the braze ring 168 (seen inFIG. 3) must be substantially equal to the cross-sectional area of thevertical braze joint 470 seen in FIG. 7. As such, the rotor shaftchamfer seat 164 is in contact with little or no braze material. One ofordinary skill in the art may calculate the amount of braze materialneeded by determining the cross-sectional area of the gap that forms theinterface between the rotor shaft 112, and the rotor body 114, arepresentative portion of which is indicated in the hatched section ofFIG. 7.

The fact that a given braze material will tend to show a greateraffinity for either the rotor shaft 112 or rotor body 114 may be used asan advantage. For example, in one instance the particular braze materialmay be selected to have an affinity for, and tend to wet rotor body 114.When the braze material is applied to form vertical braze joint 470, therotor shaft and rotor body assembly 110 may be inverted and a capillaryaction and wetting of the rotor body 114 by the braze material may bebalanced against the force of gravity. Moreover, temperature control maybe used to adjust the brazing process in order to achieve a verticalbraze joint 470 that does not wet chamfer 156 and/or chamfer seat 164.This method of providing an amount of braze material so as to only forma vertical braze joint 470 and at the same time avoid the formation ofany diagonal braze joint is one example of a step for resisting theformation of a braze joint with horizontal thermal shear.

Reference is next made to FIG. 8, which illustrates yet anotherembodiment. Here, a vertical braze joint 570, in the form of acylindrical shell, is formed between the rotor shaft 512 and the rotorbody 114. The vertical braze joint 570 has filled the space between therotor shaft 512 and the rotor body 114 from the proximal surface 148down to about the level of vertical height v of the rotor shaft chamfer556. Also, the spacing between rotor shaft main section 542 and rotorbody 114 is relatively larger than the spacing between rotor shaftchamfer 556 and rotor shaft chamfer scat 564. In the illustratedembodiment, the space or interface between the rotor shaft chamfer 556and rotor shaft chamfer seat 564 is in the form of a frusto-cone shell.

The reduced spacing between rotor shaft chamfer 556 and rotor shaftchamfer seat 564 as compared to that between rotor shaft main section542 and rotor body 114 reduces the amount of braze material neededbetween chamfer 556 and chamfer seat 564. Preferably, the spacingbetween chamfer 556 and seat 564 is less than 100 mils, and in a mostpreferred embodiment is less than about 10 mils. The first spacing(between 542 and 114) facilitates the flow of braze material, and thesecond spacing stops (or reduces) the flow of braze material.Preferably, the braze material between rotor shaft 512 and rotor body114 comprises the entire vertical braze joint 570. This embodiment mayalso be fabricated by selecting an amount of braze material that will beequivalent to the area between rotor shaft 512 and rotor body 114 abovethe level of rotor shaft chamfer 556 and rotor shaft chamfer seat 564.

In the embodiment of FIG. 8, the interface between chamfer 556 andchamfer seat 564 involves two vertical heights v and v′. In thisembodiment, v′ is less than v. The process of selecting a braze materialunder sufficient flow conditions to form a braze joint and to braze suchthat substantially no braze material fills between rotor shaft chamfer564 and rotor shaft chamfer seat 556 is another example of a step forresisting the formation of a braze joint with horizontal thermal shear.

FIG. 9 illustrates yet another embodiment of the present invention. Avertical braze joint 670 is depicted as being between a rotor shaft 612and a rotor body 614. Because capillary action of braze material underflow conditions may cause wetting to extend downwardly beyond theoccurrence of the rotor shaft chamfer 656 and the rotor shaft chamferseat 664, a rotor body depression such as a rotor body v-notch 676 andoptionally a rotor shaft v-notch 674 may be provided. Either or both ofthese v-notches act as a braze material stop or well that willaccumulate braze material and that will stop the downward flow of thebraze material during the formation of vertical braze joint 670. Thus, arotor shaft and rotor body assembly 610 comprises rotor shaft 612, rotorbody 614, rotor shaft v-notch 674, and rotor body v-notch 676 into whichvertical braze joint 670 has filled and has substantially stopped thedownward flow of braze material during formation of the assembly.

Rotor shaft v-notch 674 or rotor body v-notch 676 may be configured at alevel at or above vertical height v according to the specificapplication. Additionally, either v-notch can have an angular shape, orany other geometric configuration that may receive the excess brazematerial to a sufficient volume. In a preferred embodiment, the rotorshaft v-notch 674 and rotor body v-notch 676 may each have an angle in arange from about 90° to 30°, and most preferably about 60°. Theconfiguration of rotor shaft v-notch 674 to act as a stop or brazematerial well is an example of a means for resisting the formation of abraze joint with horizontal thermal shear.

FIG. 10 is a detail section taken from a structure at a location similarto that taken from FIG. 3 along the line 4—4 that illustrates yetanother embodiment of the present invention. In place of a rotor shaftchamfer, a rotor shaft 712 may have an enlarged portion near the rotorshaft proximal end 754. In this embodiment, the enlarged portion isdepicted as a flange 757. A vertical braze joint 770 is depicted ashaving filled against rotor shaft main section 742 beginning at proximalsurface 748 and as having terminated at a rotor body v-notch 774. Therotor body 714 has a flange seat 765 that abuts against rotor shaftflange 757.

An alternative embodiment of the invention depicted in FIG. 10 iseliminates the rotor shaft v-notch 774. In this embodiment, an amount ofbraze material is selected so as to only form vertical braze joint 770,for example as is set forth for the embodiment depicted in FIG. 7.Additionally and/or alternatively, the spacing between rotor shaft mainsection 742 and rotor body 714 and rotor shaft flange 757 and flangeseat 765 can be adjusted such that braze material flows to form verticalbraze joint 770, but is prevented from forming any horizontal thermalshear joint between flange 757 and rotor body 714. In preferredembodiments, spacing between flange 757 and flange seat may be less than100 mils, and most preferably less than 10 mils. Either or both of rotorbody v-notch 774 and spacing between rotor shaft flange 757 and theabutting portion of rotor body 714 is another example of a means forresisting the formation of a braze joint with a horizontal thermalshear.

FIG. 11 is a detail section taken from a structure at a location similarto that taken from FIG. 3 along the line 4—4 that illustrates yetanother embodiment of the present invention. In FIG. 11, it can be seenthat rotor body 114 is coupled with a rotor shaft 812 that contains adepression such as a rotor shaft v-notch 875 that acts as a stop or wellfor braze material as it flows from proximal surface 148 downwardly inthe direction of the rotor shaft chamfer 856 and rotor shaft chamferseat 164. As with other embodiments previously set forth, spacingbetween rotor shaft main section 842 and rotor body 114 may be largerthan spacing between rotor shaft chamfer 856 and rotor shaft chamferseat 164 to control the flow of braze material. Where the braze materialthat is used to form vertical braze joint 870 has a wetting affinity forrotor body 114 greater than rotor shaft 812, greater care may berequired to form vertical braze joint 870 without filling braze materialinto the space between rotor shaft chamfer 856 and rotor shaft chamferseat 164. The presence of rotor shaft v-notch 875 as well as theoptional close proximity between rotor shaft chamfer 856 and rotor shaftchamfer seat 164, that resists the flow of a selected amount of brazematerial beyond the occurrence of rotor shaft v-notch 875 is anotherexample of a means for resisting the formation of a braze joint withhorizontal thermal shear.

A depression such as a v-notch or another shape may be cut into eitherthe rotor shaft or the rotor body, or both, in order to facilitate theformation of a vertical braze joint and avoid horizontal thermal shearplanes. Additionally, other notch profiles may be formed such as a notchwith a curvilinear cross-sectional profile as opposed to a notch with arectilinear cross-sectional profile of a v-notch Other “notch”configurations that control the flow of braze material could also beused.

Presently preferred embodiments of the present invention utilize aPALCO® braze material under braze temperatures known in the prior art.Other materials could also be used.

To summarize, embodiments of the present invention have distinctadvantages over that of the prior art. One advantage is that the partsare more easily machined because there is no thread-cutting operation,either for the rotor shaft where external threads were previouslyrequired, or for the rotor body where internal threads were previouslyrequired. As a result of the absence of threads, the parts are moreeasily machined and also easier to assemble.

Another distinct advantage is that no special welding or bondingtechniques are required such as electron beam welding often required inthe prior art. The absence of any special welding or bonding techniquesalso eliminates destructive embrittlement of the interface between therotor shaft and rotor body. Another distinct advantage of embodiments ofthe present invention is that they eliminate substantially all thermalsheer stresses in the rotor braze joint. This greatly increases theoperational life of the assembly.

Another distinct advantage of embodiments of the present invention isthat the rotor shaft and rotor body assembly allows the x-ray tube to beoperated at higher temperatures. Substantially no thermal sheer isexperienced to compromise the integrity of the braze joint. Moreover,even if the braze joint is compromised, the rotor shaft and rotor bodyassembly will not de-couple because of the chamfer or flange featurethat holds the assembly together regardless of the presence or absenceof the braze joint.

The present invention may be embodied in other specific forms withoutdeparting from its spirit or essential characteristics. The describedembodiments are to be considered in all respects only as illustrated andnot restrictive. The scope of the invention is, therefore, indicated bythe appended claims rather than by the foregoing description. Allchanges which come within the meaning and range of equivalency of theclaims are to be embraced within their scope.

What is claimed and desired to be secured by United States LettersPatent is:
 1. An x-ray tube having a rotating anode, comprising: a rotorshaft having a main section operatively connected to the rotating anode,and an engagement end having a predefined profile; and a rotor bodyhaving an axial bore formed therethrough, the bore having inner recesshaving a shape that is substantially complimentary to the shape of theprofile of the engagement end, wherein a connection interface isprovided between the rotor shaft and the rotor body when the engagementend is operably received within the inner recess.
 2. An x-ray tubeaccording to claim 1, wherein the profile of the engagement end issubstantially convex in shape.
 3. An x-ray tube according to claim 1,further comprising: a braze joint that is substantially axially disposedbetween the rotor shaft and the rotor body along at least a portion ofthe connection interface.
 4. An x-ray tube according to claim 1, whereinthe engagement end is a flange.
 5. An x-ray tube according to claim 1,further comprising: a depression formed along at least a portion of theinner recess at a location substantially proximate to the connectioninterface.
 6. An x-ray tube according to claim 1, further comprising: adepression formed along at least a portion of the rotor shaft at alocation substantially proximate to the connection interface.
 7. Anx-ray tube according to claim 1, wherein at least a portion of the innerrecess has a size and a shape such that a tight compression fit isprovided between the rotor shaft and the rotor body when the engagementend is received within the inner recess.
 8. An x-ray tube according toclaim 1, wherein at least a portion of the inner recess has a size andshape such that a gap is provided between the rotor shaft and the rotorbody when the engagement end is received within the inner recess.
 9. Anx-ray tube according to claim 8, wherein the dimension of the gap isselected so that a predetermined amount of braze material is capable ofbeing disposed within the connection interface.
 10. An x-ray tubeaccording to claim 8, wherein the width of the gap varies in a manner soas to substantially preclude braze material from being received withinpredetermined regions of the connection interface.
 11. An x-ray tubecomprising: a rotary anode; a rotor shaft having a first end operablyattached to the rotary anode, and a second end having a predefinedprofile; a rotor body having an axial bore passing through a centralportion of the rotor body, wherein the axial bore includes a coaxialrecess that is adapted to form a substantially complimentary matingsurface with at least a portion of the rotor shaft and the second end ofthe rotor shaft; and a braze joint axially disposed along at least aportion of the mating surface between the rotor shaft, the second endand the recess in the rotor body.
 12. An x-ray tube comprising: a rotorshaft having a cylindrical main section that is axially disposed in anevacuated housing; a rotor body axially disposed in the x-ray tube andhaving an axial bore formed therein that is capable of receiving therotor shaft main section; and means for retaining the rotor shaft in theaxial bore formed within the rotor body.
 13. An x-ray tube according toclaim 12, wherein the means for retaining the rotor shaft comprises achamfer formed on an end of the rotor shaft that has a correspondingmating surface within the axial bore.
 14. An x-ray tube according toclaim 12, wherein the means for retaining the rotor shaft comprises aflange formed on an end of the rotor shaft that has a correspondingmating surface within the axial bore.
 15. An x-ray tube according toclaim 12, further comprising: means for substantially resisting theformation of a braze joint having a horizontal thermal shear component.16. An x-ray tube according to claim 15, wherein the means forsubstantially resisting the formation of a braze joint comprises atleast one depression formed within the rotor body axial bore.
 17. Anx-ray tube according to claim 16, wherein the depression comprises aV-notch formed along the inner periphery of the rotor body axial bore.18. An x-ray tube according to claim 15, wherein means for substantiallyresisting the formation of a braze joint comprises a depression formedalong at least a portion of the outer periphery of the rotor shaft. 19.An x-ray tube according to claim 18, wherein the depression comprises aV-notch formed along the outer periphery of the rotor shaft.
 20. Amethod of manufacturing a rotor body and a rotor shaft for use in anx-ray tube, the method comprising; forming a rotor shaft with anengagement end having a predefined shape; forming a rotor body with anaxial bore having an inner recess that provides a complementary shape tothat of the engagement end; and inserting a first portion of the rotorshaft through the rotor body axial bore until the engagement end forms aconnection interface with the inner recess.
 21. A method ofmanufacturing according to claim 20, further comprising the step of:creating a temperature differential between the rotor shaft and therotor body that is sufficient to allow the rotor shaft to pass throughthe axial bore, whereby a tight compression fit is provided between atleast a portion of the engagement end and the inner recess when thetemperature differential is removed.
 22. A method of manufacturingaccording to claim 20, further comprising the step of: brazing the rotorshaft to the rotor body in the region of the connection interface.
 23. Amethod of manufacturing according to claim 22, wherein the brazing stepcomprises the steps of: providing a braze ring to rest against the rotorshaft and against the rotor body; and heating the braze ring sufficientto cause it to flow between the rotor shaft and the rotor body in theregion of the connection interface.
 24. A method of manufacturingaccording to claim 22, wherein the brazing step comprises the steps of:providing a braze ring that encircles the rotor shaft and rests upon therotor body; heating the braze ring to cause it to flow and to fillbetween the rotor shaft and the rotor body; inverting the rotor shaftand the rotor body; and controlling the flow of the braze ring to form abraze joint having a predetermined orientation within the correctioninterface.
 25. A method of manufacturing according to claim 20, furthercomprising the steps of: providing a first gap between the rotor shaftand the axial bore in the region of the connection interface; providinga second gap between the rotor shaft and the axial bore, wherein thesecond gap is smaller than the first gap; and flowing braze materialinto the first gap under conditions that the material fills the firstgap but does not fill the second gap.
 26. A method of manufacturingaccording to claim 20, further comprising the steps of: causing brazematerial to flow between the rotor shaft and the rotor body in apredetermined region of the connection interface.
 27. A method ofmanufacturing according to claim 20, wherein the braze material forms abraze joint that is substantially devoid of horizontal shear stressbetween the rotor shaft and the rotor body.